A canted log, or "cant", by definition has first and second opposed cut planar faces. In the prior art, cants were fed linearly through a profiler or gang saw so as to produce at least a third planar face either approximately parallel to the center line of the cant, so called split taper sawing, or approximately parallel to one side of the cant, so called full taper sawing; or at a slope somewhere between split and full taper sawing. For straight cants, using these methods for volume recovery of the lumber can be close to optimal. However, logs often have a curvature and usually a curved log will be cut to a shorter length to minimize the loss of recovery due to this curvature. Consequently, in the prior art, various curve sawing techniques have been used to overcome this problem so that longer length lumber with higher grade recovery may be achieved.
Curve sawing typically uses a mechanical centering system that guides a cant into a secondary break-down machine with chipping heads or saws. This centering action results in the cant following a path very closely parallel to the center line of the cant, thus resulting in split taper chipping or sawing of the cant. Cants that are curve sawn by this technique generally produce longer, wider and stronger boards than is typically possible with a straight sawing technique where the cant has significant curvature.
Curve sawing techniques have also been applied to cut parallel to a curved face of a cant, i.e. full taper sawing. See for example Kenyan, U.S. Pat. No. 4,373,563 and Lundstrom, Canadian Patent No. 2,022,857. Both the Kenyan and Lundstrom devices use mechanical means to center the cant during curve sawing and thus disparities on the surface of the cant such as scars, knots, branch stubs and the like tend to disturb the machining operation and produce a "wave" in the cant. Also, cants subjected to these curve sawing techniques tend to have straight sections on each end of the cant. This results from the need to center the cant on more than one location through the machine. That is, when starting the cut, the cant is centered by two or more centering assemblies until the cant engages anvils behind the chipping heads. When the cant has progressed to the point that the centering assemblies in front of the machine are no longer in contact, the cant is pulled through the remainder of the cut in a straight line. It has also been found that full taper curve sawing techniques, because the cut follows a line approximately parallel to the convex or concave surface of the cant, can only produce lumber that mimics these surfaces, and the shape produced may be unacceptably bowed.
Thus in the prior art, so called arc-sawing was developed. See for example U.S. Pat. Nos. 5,148,847 and 5,320,153. Arc sawing was developed to saw irregular swept cants in a radial arc. The technique employs an electronic evaluation and control unit to determine the best semi-circular arc solution to machine the cant, based, in part, on the cant profile information. Arc sawing techniques solve the mechanical centering problems encountered with curve sawing but limit the recovery possible from a cant by constraining the cut solution to a radial form.
Applicant is aware of attempts in the prior art to curve sawing by pivoting or skewing the gangsaw, and in particular, U.S. Pat. No. 4,599,929 which issued to Dutina. Dutina teaches curve sawing where each saw guide and/or saw axle is adjusted in view of the average inclination over the sawing line of the entire longitudinal profile of the workpiece or of parts of the longitudinal profile.
Applicant is also aware of U.S. Pat. No. 4,373,563, U.S. Pat. No. 4,572,256, U.S. Pat. No. 4,881,584, U.S. Pat. No. 5,320,153, U.S. Pat. No. 5,400,842 and U.S. Pat. No. 5,469,904, which all relate to the curve sawing of two-sided cants.
It has been found that optimized lumber recovery is best obtained for most if not all cants if a unique cutting solution is determined for every cant. Thus for each cant a "best" curve is determined, which in some instances is merely a straight line parallel to the center line of the cant, and in other instances a complex curve that is only vaguely related to the physical surfaces of the cant.
Thus it is an object of the present invention to improve recovery of lumber from cants and in particular irregular or crooked cants by employing a "best" curve and a unique cutting solution for each cant. To achieve this objective a two-sided cant is positioned and accurately driven straight into an active curve sawing gang, to produce the "best" curve which includes smoothing technology.
A board, or "flitch", by definition has first and second opposed cut planar faces and first and second opposed waned edges. In one prior art method, flitches would be scanned and sequenced horizontally then positioned in the desired skew, if any, and then clamped by feed rolls to be fed linearly into a conventional edger. In a second prior art method, flitches would be centered in the direction of flow and then translated through a linear scanner and, in the same direction, into a conventional edger. The first approach is effective, but the system is quite expensive and the positioning of the flitch takes extra time. The second approach works for uniform straight flitches, but causes a loss of recovery when the flitches are crooked or flared on one side.
Different methods of lineal scanning and positioning have been proposed. U.S. Pat. No. 4,239,072 (Merilainen) discloses a lineal scanning and skew edging process. It lacks the ability to produce high quality chips at higher feed speeds and does not allow for multiple saws. U.S. Pat. No. 4,449,557 (Makela) discloses a similar process, but without the ability to reduce the edgings to chips. It also does not allow for multiple saws.
U.S. Pat. No. 5,429,161 (Allard) discloses a linear scanning edger process. The apparatus positions the flitch while the flitch is moving, with two pairs of tandem (top and bottom) clamp rollers that skew the flitch as it is moving up to the edger. This process relies on the twisting of the flitch as it moves through the roller clamps, which causes skidding of the flitch between the rollers as they are skewed. The variance in friction between different flitches and the rollers and the difference in the direction of the rollers' axis and the direction of the flitch as it travels through the roller clamps, can cause a margin of error that reduces the recovery percentage.
It has been found that optimized lumber recovery is more easily obtained by merely roughly, that is, non-accurately, placing the flitch or other workpiece on a conveyor, then conveying the flitch or workpiece through a lineal scanner, and straight through an edger where, instead of positioning the flitch, the saws and chip heads adjust and then traverse, to saw and chip the flitch. Because chip heads replace the outer saws, the need to handle the edgings after they exit the edger is eliminated. This eliminates a "tailer" which is normally used to separate the edgings and also the need for extra conveyors to transport the edgings.
The present invention skews the saws and guides about a vertical axis perpendicular to the flow by skewing the sawbox and translates the saws and guides transversely to the flow within the sawbox, that is, relative to the sawbox, to accomplish active curve sawing of a workpiece.
It is an object of the present invention to improve the efficiency of lumber production from workpieces, and in particular from irregular or crooked workpieces. A workpiece moves straight in the direction of flow through the curve sawing sawbox, where the saws and/or chip heads skew and actively translate in unison to saw and/or chip the flitch.
It is a further object of the present invention to improve the efficiency of the lumber production from flitches and in particular for irregular or crooked flitches, by employing scanning and a traversing edger which follows the cutting solution for each flitch as is determined by the optimizer from the scanned profile of the flitch and the desired lumber sizes. This objective is achieved by not positioning the flitch with extra machinery, but rather to place the flitch approximately correctly positioned and then feed the flitch through a scanner and then into an edger, adjusting the skew and then actively traversing the edger, to produce the desired recovery percentage.
It is also an object of the present invention to provide: (a) a sawbox capable of variable lumber target sizes, that allows the setting of different saw blade spacings thereby reducing the number of saw blades needed in mills where lumber widths vary, (b) a sawbox of reduced weight and size capable of larger sawing zones, (c) a sawbox requiring less travel because of its increased sawing zone capability, and, (d) a sawbox having a reduced response time.
It is another object of the present invention to eliminate, by the use of chip heads within the active curve sawing edger, the need to handle edgings behind the sawbox and at the same time improving the chip quality produced from the edgings.